1. Field of the Invention
The proposed invention relates to reducing energy consumption of inductive loads. More particularly it is apparatus for and a method of reducing energy consumption of fluorescent and other ballasted inductive lighting loads such as high intensity discharge (HID) lamps without significantly reducing load voltage or light output and also for reducing energy consumption of inductive AC motors.
2. Background Art
Prior art implementations of energy saving devices for fluorescent lighting loads have generally not provided arbitrary load voltage switching or commutating current paths. Most of these devices employ a silicon controlled rectifier (SCR) in a conventional mode which prohibits arbitrary load voltage switching. When used in this mode the SCR acts as a switch to the downstream load. This switch can be turned on arbitrarily but can only be turned off when the load voltage reverses polarity. Resulting load voltage wave forms are as shown in prior art FIG. 1.
The disadvantage of the SCR load voltage wave form with the ballasted inductive load of fluorescent lighting is the relatively low RMS load voltage that results when the lighting load is controlled to obtain appreciable energy savings. Because the SCR switch can only be turned on after zero crossover the load voltage must remain off for relatively long periods within a half-cycle to realize appreciable power savings. The resulting low RMS load voltage in fluorescent lighting is undesirable from a bulb life standpoint and to insure adequate firing of the fluorescent bulbs from a cold start. Indeed most SCR fluorescent lighting devices cannot restart fluorescent lights if they are switched off without first applying full power and returning to the switched wave form mode. This is a distinct disadvantage for a multiple switched fluorescent load.
The proposed invention overcomes many of these disadvantages by switching only a small portion of the wave form to achieve appreciable energy savings. The result is load voltage with a relatively high RMS value at appreciable power savings.